Vertical spacing between arrow and caption with unicode-math

Question

When using unicode-math and arrow captions (most prominently with extarrows), the vertical spacing between the arrows and the text increases a lot:

\documentclass{article}

\usepackage{amsmath,extarrows}

\usepackage{fontspec}
%\usepackage{unicode-math}

\begin{document}
   \[ \xLongrightarrow{\text{This is a test}} \]
\end{document}

Without unicode-math the result is

;

however, with unicode-math, the result becomes

.

This holds true for all the extensible arrows; however, the spacing in \xlongequals remains fine.

By default, these examples all use Latin Modern, so the extension character fits to the arrow head unlike in some other fonts. Is this perhaps a unicode-math bug or is the position information in the OTF fonts wrong, which causes such a misalign? (Basically, the problem is also there for \xrightarrow, so it does not seem to be a problem of extarrows in particular.)

The result is the same both in LuaLaTex and XeLaTeX.